Thanks for the scene, I'm investigating your issue. Perhaps there is a bug in the code that processes the UDIM filenames, but meanwhile ... can you please check what happens if you set the grid size to 10x10?

Sorry for the late reply. I've found and fixed the problem with the UDIM files in the plugin. It was a tricky issue related to the filenames order in the udim texture node. I'll include this fix in the upcoming new Octane 4.03 and 2018.1 builds.